Wireless terminal such as mobile phone comprises RF (Radio Frequency) signal line. The RF signal line is normally made of coaxial cable. Such RF signal line made of coaxial cable makes the inner space of the wireless terminal narrower so that flexible circuit board generally applied to the wireless terminal nowadays.
Wireless terminal such as mobile phone comprises RF (Radio Frequency) signal line. The RF signal line is normally made of coaxial cable. Such RF signal line made of coaxial cable makes the inner space of the wireless terminal narrower so that flexible circuit board generally applied to the wireless terminal nowadays.
In the case of traditional flexible circuit board, it is possible that flexible circuit board is apt to be fracture or broke down in the part of repeatedly bending such as folding type handset. In order to overcome such a problem, the thickness of the flexible circuit board changes by providing with a dielectric with only a certain section in the longitudinal direction. In this case, a method of cutting the dielectric by a blade, a laser or the like is used to make the dielectric exist only in a predetermined section.
However, when the dielectric is cut, a part of the signal line and the ground surface is also cut and damaged, so that the signal transmission efficiency is lowered. Therefore, the damaged part thereof is cut off due to repeatedly bending.
In addition, a common method of cutting with a laser beam causes carbide to be formed on a signal line and a ground, so that a signal line and a ground are connected electrically, or signal transmission efficiency is lowered.
On the other hand, flexible circuit board makes sure of the necessary amount of signals by the means of increasing the size of signal line, decreasing line loss at signal transmission through thicken the signal line, or decreasing the signal loss of reflection by shielding the external environmental signals from outside.
Flexible circuit board has optimum impedance of about 33Ω at the signal transmitter, and optimum impedance of about 75Ω at the signal receiver. Considering both the transmitter and receiver, it is ordinary that flexible circuit board should be designed to have characteristic impedance of about 50Ω.
In the case that external environmental signals are introduced from other outside components, the characteristic impedance would be deviated from the normal level of 50Ω, so that the signal transmission efficiency might be aggravated.
Therefore, flexible circuit board should be applied at the reasonably separated location from other components so as to prevent unwanted impedance variation. In this case, however, the inner space of the terminal, which is the main merit and advantage of flexible circuit board, may be narrower.
Flexible circuit board may be placed near other components by the impedance matching. But, in this case, the shape of flexible circuit board should be changed as well, according to the variation of shape or location of at least one component among its main board, sub board, battery or so. Therefore, it is necessary that the flexible circuit board can be installed freely inside of the wireless terminal without effect of other components thereof.
The background described herein will be understood only for the purposes of understanding of background of the invention, so that said background should not be accepted the prior art of the invention in the view of the person having ordinary skilled in the art.